Analytical calculus and Monte Carlo simulation of crosslinked polymer formation in the copolymerization of tetraethoxysilane and poly(dimethylsiloxane)

Abstract

Full Paper: To understand the fundamental aspects of the polycondensation reaction of hydrolyzed tetraethoxysilane (TEOS) and silanol-terminated poly(dimethylsiloxane) (PDMS), we modeled the reaction system as a stepgrowth polymerization of A4 and polydisperse A2 , assuming the reactivities of all functional groups are equal. The analytical solution for the weight-average molecular weight is developed, and in addition, a Monte Carlo simulation is conducted to investigate the detailed structural development. It was found that as long as the molecular weight of PDMS is much larger than TEOS, the apparent behavior is significantly different from usual gelling systems. The gel point is relatively insensitive to the weight fraction of crosslinker (TEOS), the polydispersity index may decrease during polymerization before the rapid increase to infinity, and the molecular weight distribution profile may not show a significant broadening toward gelation. Even though the present model assumes a complete random reaction process among functional groups, formation of a heterogeneous structure in which a tight core consisting of TEOS-based molecules is surrounded by soft PDMS chains was observed in the Monte Carlo simulation.